Catalytic oxidation of alkaline pulping liquor

ABSTRACT

An alkaline sulfide containing paper pulping liquor is treated with an oxygen containing gas in the presence of a catalytic metal compound selected from metal oxides and metal sulfides, so as to form polysulfide for increased efficiency in paper pulping. The catalytic metal compound is employed in such a manner that intimate contact of the oxygen in the gas, the sulfide containing liquor, and the catalyst takes place.

United States Patent [1 Barker et al.

[ 1 Jan; 14, 1975 CATALYTIC OXIDATION OF ALKALINE PULPING LIQUOR Inventors: Richard G. Barker, Princeton Junction, N.J.; Edward S. Becker, Delta, British Columbia, Canada Assignee: Union Camp Corporation, Wayne,

Filed: Dec. 14, 1973 AppL No.: 424,671

Related U.S. Application Data Continuation of Ser. No. 154,356, June 18, 1971, abandoned.

U.S. Cl. 162/79, 162/82 Int. Cl. D2lc 3/24 Field of Search 162/79, 82, 83; 23/134,

References Cited UNITED STATES PATENTS 3,216,887 11/1965 Landmark 162/82 X 3,470,061 9/1969 Barker 162/83 X 3,573,157 3/1971 Cook 3,653,824 4/1972 Barker et a1. 423/49 Primary ExaminerS. Leon Bashore Assistant ExaminerArthur L. Corbin Attorney, Agent, or Firm--Kane, Dalsimer, Kane, Sullivan and Kurucz [57] ABSTRACT 29 Claims, 2 Drawing Figures BACKGROUND OF THE INVENTION The use of polysulfide for pulping of wood to be formed into paper products is known in the art. For example, in U.S. Pat. No. 3,470,061 Barker, assigned to the same assignee as the present invention, the formation of polysulfide by treatment of a sulfide bearing liquor with an oxidizing metallic compound is described. Following oxidation of the sulfide values to polysulfide, the now reduced compounds must be removed from the liquor and regenerated in order that they may be reused. A process for the regeneration, and equipment to be utilized in that regeneration, are

described and claimed in the copending application of Richard G. Barker and James L Ma, Ser. No. 867,057, filed Oct. 16, 1969, now U.S. Pat. No. 3,653,824 and assigned to the same assignee as the present invention. According to that application, the reduced metal compounds are treated in a particular manner in order to oxidize them so as to be useful in a further oxidation of the sulfide values in a paper pulping solution to polysulfide.

Different methods of forming polysulfides are described in Landmark U.S. Pat. No. 3,216,887 and in Domtar Canadian Pat. No. 815,432. These processes are subject to certain disadvantages.

In accordance with the present invention it has unexpectedly been discovered that the sulfide values in a paper pulping liquor, particularly a white liquor, may be continuously oxidized to polysulfides employing air, or another oxygen containing gas, as the oxidizing medium, in the presence of a catalytic metal compound. In some cases, the catalytic metal compound may be the same as that employed in the previouslyreferenced Barker patent. Because the metal compound is employed as a catalyst, rather than directly oxidizing the sulfide values, with consequent reduction of the metallic compound, no regeneration is necessary. Therefore, a much smaller amount of solid material is required than that recited in previously referenced copending application Ser. No. 867,057 and, consequently, there are significant savings in equipment and processing with regard to solid separation and regeneration.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 illustrates a process flow according to one embodiment of my invention; and

FIG. 2 represents a process flow according to a second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with the present invention a paper pulping liquor is oxidized with air, or another oxygen containing gas, in the presence of a catalytic metal compound. The oxidation is carried out in such a manner that there is intimate contact between the oxygen containing gas, the pulping liquor, and the catalytic metal compound. The particular paper pulping liquor employed is a white liquor.

While the sulfidity of the liquor is not critical, best results are obtained when the liquor has a sulfidity of from 20 to 40%, preferably from 25 to 35%. The sulfide concentration of the liquor may range from 20 to 50 grams per liter, preferably from 40 to 50 grams per liter.

The flow rate of the oxygen containing gas is not critical, nor is the particular gas mixed with the oxygen, except that the additional gas should be inert to the reactants under the conditions of reaction. For economic reasons, it is preferred to employ air. There may be from I to 30 liters of oxygen per hour for each liter of paper pulping liquor being processed. Preferably, there are from about 1.5 to 2.5 liters of oxygen per hour for each liter of paper pulping liquor. Additionally, the oxygen containing gas preferably contains from 5 to 2l% oxygen.

The liquor is generally heated before passing into the oxidation chamber. In general, the liquorshould be at a temperature of from 50to 90C., preferably from to C. I

In the first embodiment of the invention, as illustrated in FIG. 1, the paper pulping liquor is pumped to the bottom of a reaction tower and flows countercurrently to the catalytic metal compound. The oxygen containing gas is bubbled intothe reactionv tower near the bottom. The catalyst, being denser than the liquor, falls to the bottom of the reaction tower and is removed as a slurry. This slurry is recycled to the tower, preferably at a point above the midway mark of the tower, and most preferably at about the two-thirds level of the tower. No reconditioning or further processing of the catalyst is necessary. The oxidized polysulfide liquor is continuously removed from the top of the tower.

In a second embodiment of the invention, according to FIG. 2, a packed tower is employed. The packed tower may contain large particles of the catalytic metal compound, or the packing may be standard tower packing, such as Raschig rings, Beryl saddles, etc. which have been coated with the catalytic metal compound. The paper pulping liquor is continuously pumped to the bottom of the tower, air is continuously fed to the bottom of the tower, and the oxidized polysulfide liquor is continuously removed from the top of the tower.

With the first embodiment, employing the recirculating catalyst slurry, there should be from 0.1 to 75 parts of the catalytic metal compound for each parts of alkali metal sulfide present in the initial paper pulping liquor. Preferably, there are from 5 to 10 parts of the catalytic metal compound for each 100 parts of the alkali metal sulfide.

In general, any equipment may be used which provides a reaction zone in'which the oxygen containing gas, catalyst, and sulfide pulping liquor are intimately mixed, and in which the three components intimately contact each other. The figures illustrate two types of equipment which provide for such a reaction zone.

Whichever of the concepts are employed, various catalytic metal compounds can be employed including metal oxidesor metal sulfides. Of the former, the metal moiety is preferably selected from the class consisting of manganese, copper, iron, cobalt, zinc, aluminum, nickel and chromium, while with the latter the metal moiety is preferably selected from the class consisting of manganese, nickel, copper, iron and cobalt. Preferably, the catalytic metal compound is manganese dioxide.

The process acccording to the present invention will be described in greater detail in the following examples. These examples should be considered as illustrative only, and not as limiting in any way the full scope of the invention as covered in the appended claims.

EXAMPLE 1 in this example a white liquor with a sulfidity of 30%, containing 3 8 grams per liter of sodium sulfide was oxidized according to the process illustrated in FIG. 1. The oxidation was carried out at 70C., employing air at a rate so as to provide 5.9 liters of oxygen per liter of liquor per hour. Manganese dioxide was employed as the catalyst and the catalyst slurry was recirculated at such a rate as to provide parts of the catalyst for each 100 parts of sodium sulfide. Following generation of polysulfide in the reaction tower, the white liquor was employed to pulp wood, the resulting black liquor treated and recirculated to the tower as white liquor. The polysulfide level of the white liquor exiting from the reaction tower was measured, at intervals as indicated in Table l:

Elapsed Hours Polysulfide, Grams Per Liter of Sulfur Thus, it can be seen that the sodium sulfide in the white liquor is continuously oxidized to polysulfide with essentially no loss in catalytic activity.

EXAMPLE 2 EXAMPLE 3 In this example white liquor containing 32.7 grams per liter of sodium sulfide was oxidized with air at room temperature. The flow rate of air was such as to provide 29.7 liters of oxygen per liter of oxygen per liter of liquor per hour. Nickel sulfide was employed as the catalyst in a ratio of 1 part of the catalyst for each 100 parts of sodium sulfide. Within 4 hours of process operation, the polysulfide sulfur content was 7.1 grams per liter.

EXAMPLE 4 The same white liquor as employed in Example 3 was processed according to this example utilizing, as the oxygen containing gas, a mixture containing 5 parts oxygen and 95 parts nitrogen, by weight. The flow rate of the mixture was such as to provide oxygen at a ratio of 2.1 liters per liter of liquor per hour. The catalyst employed was manganese dioxide in a ratio of 2.5 parts for each 100 parts, by weight, of sodium sulfide. Conditions of reaction were otherwise the same as in Example 1. Within 3 hours of process operation, the polysulfide sulfur concentration was 4.9 grams per liter.

The invention has been described in detail with particular reference made to various preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. In a process for converting the sulfide in paper pulping liquor to polysulfide liquor by oxidation with a gas selected from oxygen and oxygen containing gases, the improvement which comprises catalyzing said oxidation with a catalyst selected from metal oxides and metal sulfides.

2. A process according to claim 1 wherein said catalyst is employed in a proportion within the range of from 0.1 to parts by weight for each 100 parts of alkali metal sulfide present in the starting paper pulping liquor.

3. A process according to claim 1 wherein said catalyst is employed in a proportion within the range of from 5 to 10 parts by weight for each 100 parts of alkali metal sulfide present in the starting paper pulping liquor.

4. A process according to claim 1 wherein said catalyst is selected from the oxides of manganese, copper, iron, cobalt, zinc, aluminum, nickel and chromium.

5. A process according to claim 1 wherein said catalyst is selected from the sulfides of manganese, nickel, copper, iron and cobalt.

6. A process according to claim 1 wherein said catalyst is manganese dioxide.

7. A process according to claim 1 wherein said catalyst is manganous sulfide.

8. A process according to claim 1 wherein said catalyst is nickel sulfide.

9. A process for oxidizing the sulfide in a paper pulping liquor to polysulfide liquor which comprises; contacting said sulfide with oxygen gas in the presence of a catalyzing amount of a catalyst selected from a metal oxide and a metal sulfide.

10. A process according to claim 9 wherein said sulfide is present in the starting liquor in a concentration of from 20 to 50 grams per liter.

11. A process according to claim 9 wherein said reaction is carried out at a temperature between about 50C. to about C.

12. A process according to claim 9 wherein sodium sulfide is oxidized to obtain sodium polysulfide.

13, A process according to claim 9 wherein said catalyst is employed in a proportion within the range of from about 0.1 to 75 parts by weight for each parts of alkali metal sulfide present in the starting paper pulping liquid.

14. A process according to claim 9 wherein said catalyst is employed in a proportion within the range of from about 5 to l0-parts by weight for each 100 parts of alkali metal sulfide present in the starting paper pulping liquor.

15. A process according to claim 9 wherein said catalyst is selected from the oxides of manganese, copper, iron, cobalt, zinc, aluminum, nickel and chromium.

16. A process according to claim 9 wherein said catalyst is selected from the sulfides of manganese, nickel, copper, iron and cobalt.

17. A process according to claim 9 wherein said catalyst is manganese dioxide.

18. A process according to claim 9 wherein said catalyst is manganous sulfide.

19. A process according to claim 9wherein said catalyst is nickel sulfide.

20. A process for oxidizing a sulfide containing paper pulping liquor to obtain polysulfide liquor therein which comprises:

a. passing the sulfide containing liquor through a reaction zone;

b. simultaneously passing a gas selected from oxygen and oxygen containing gasses through said reaction zone so as to intimately contact said sulfide containing paper pulping liquor, whereby oxidation of said sulfide occurs; and

c. catalyzing said oxidation with a catalyst selected from a metal oxide and a metal sulfide, and,

d. removing polysulfide liquor from said reaction zone.

21. The process of claim wherein said catalyst is recirculated through said reaction zone.

22. The process of claim 21 wherein said catalyst is recirculated as a slurry.

23. The process of claim 21 wherein said catalyst is recirculated countercurrently to said liquor and said gas.

24. The process of claim 21 wherein said catalyst is selected from the oxides of manganese, copper, iron, cobalt, zinc, aluminum, nickel and chromium and the sulfides of manganese, nickel, copper, iron and cobalt.

25. The process of claim 24 wherein the catalyst is manganese dioxide.

26. The process of claim 20 wherein the catalyst is in a fixed bed within said reaction zone.

27. The process of claim 26 wherein said catalyst is selected from the oxides of manganese, copper, iron, cobalt, zinc, aluminum, nickel and chromium and the sulfides of manganese, nickel, copper, iron and cobalt.

28. The process of claim 26 wherein said catalyst is manganese dioxide.

29. A process according to claim 26 wherein the reaction zone is within a tower. 

2. A process according to claim 1 wherein said catalyst is employed in a proportion within the range of from 0.1 to 75 parts by weight for each 100 parts of alkali metal sulfide present in the starting paper pulping liquor.
 3. A process according to claim 1 wherein said catalyst is employed in a proportion within the range of from 5 to 10 parts by weight for each 100 parts of alkali metal sulfide present in the starting paper pulping liquor.
 4. A procEss according to claim 1 wherein said catalyst is selected from the oxides of manganese, copper, iron, cobalt, zinc, aluminum, nickel and chromium.
 5. A process according to claim 1 wherein said catalyst is selected from the sulfides of manganese, nickel, copper, iron and cobalt.
 6. A process according to claim 1 wherein said catalyst is manganese dioxide.
 7. A process according to claim 1 wherein said catalyst is manganous sulfide.
 8. A process according to claim 1 wherein said catalyst is nickel sulfide.
 9. A process for oxidizing the sulfide in a paper pulping liquor to polysulfide liquor which comprises; contacting said sulfide with oxygen gas in the presence of a catalyzing amount of a catalyst selected from a metal oxide and a metal sulfide.
 10. A process according to claim 9 wherein said sulfide is present in the starting liquor in a concentration of from 20 to 50 grams per liter.
 11. A process according to claim 9 wherein said reaction is carried out at a temperature between about 50*C. to about 90*C.
 12. A process according to claim 9 wherein sodium sulfide is oxidized to obtain sodium polysulfide.
 13. A process according to claim 9 wherein said catalyst is employed in a proportion within the range of from about 0.1 to 75 parts by weight for each 100 parts of alkali metal sulfide present in the starting paper pulping liquid.
 14. A process according to claim 9 wherein said catalyst is employed in a proportion within the range of from about 5 to 10 parts by weight for each 100 parts of alkali metal sulfide present in the starting paper pulping liquor.
 15. A process according to claim 9 wherein said catalyst is selected from the oxides of manganese, copper, iron, cobalt, zinc, aluminum, nickel and chromium.
 16. A process according to claim 9 wherein said catalyst is selected from the sulfides of manganese, nickel, copper, iron and cobalt.
 17. A process according to claim 9 wherein said catalyst is manganese dioxide.
 18. A process according to claim 9 wherein said catalyst is manganous sulfide.
 19. A process according to claim 9 wherein said catalyst is nickel sulfide.
 20. A process for oxidizing a sulfide containing paper pulping liquor to obtain polysulfide liquor therein which comprises: a. passing the sulfide containing liquor through a reaction zone; b. simultaneously passing a gas selected from oxygen and oxygen containing gasses through said reaction zone so as to intimately contact said sulfide containing paper pulping liquor, whereby oxidation of said sulfide occurs; and c. catalyzing said oxidation with a catalyst selected from a metal oxide and a metal sulfide, and, d. removing polysulfide liquor from said reaction zone.
 21. The process of claim 20 wherein said catalyst is recirculated through said reaction zone.
 22. The process of claim 21 wherein said catalyst is recirculated as a slurry.
 23. The process of claim 21 wherein said catalyst is recirculated countercurrently to said liquor and said gas.
 24. The process of claim 21 wherein said catalyst is selected from the oxides of manganese, copper, iron, cobalt, zinc, aluminum, nickel and chromium and the sulfides of manganese, nickel, copper, iron and cobalt.
 25. The process of claim 24 wherein the catalyst is manganese dioxide.
 26. The process of claim 20 wherein the catalyst is in a fixed bed within said reaction zone.
 27. The process of claim 26 wherein said catalyst is selected from the oxides of manganese, copper, iron, cobalt, zinc, aluminum, nickel and chromium and the sulfides of manganese, nickel, copper, iron and cobalt.
 28. The process of claim 26 wherein said catalyst is manganese dioxide.
 29. A process according to claim 26 wherein the reaction zone is within a tower. 